then perform a Shared Nothing Live Migration of the virtual machine from the
Windows Server 2012 R2 host to the Windows Server 2016 host. For the first time, it’s
possible to perform a cross-version Live Migration. This allows you to move the
virtual machines to Windows Server 2016 with no downtime to the virtual machine at
all. Many companies use a type of rolling upgrade approach, provided that they have
one spare server available to use. In this process, a new box is stood up with Windows
Server 2016, and the virtual machines from a host are migrated to this new box. The
host that is now emptied is then reinstalled with Windows Server 2016, and the VMs
from another host are moved to this newly installed host, and the process continues.
Note that while this process is targeted for Windows Server 2012 R2 to Windows
Server 2016 with no downtime, you could use the same process from Windows Server
2012, except there would be some downtime as part of the virtual machine migration
and a storage migration or an export/import would be performed between hosts. If the
stand-alone hosts were using SAN storage, it would be possible just to unmask the
LUNs used by the source host to the target host and then import the virtual machines.
Clusters
Most production Hyper-V environments will not be stand-alone hosts but rather have
clusters of Hyper-V hosts.
Failover Clustering provides the ability to migrate workloads between a source and
target cluster, and Hyper-V virtual machines are a supported workload that can be
migrated. The way that the Cluster Migration Wizard works is that you tell the wizard
that runs on the target Windows Server 2016 cluster that you wish to migrate roles
and then point the wizard to the old Windows Server 2012 or Windows Server 2012 R2
cluster. The wizard then shows the roles running on specific storage volumes and
disconnects the storage from the old cluster, activates on the new cluster, and
migrates the roles (virtual machines) that are hosted on that storage. It’s important to
ensure that the switches have been zoned correctly so that the target cluster has rights
to access the migrated LUNs, and the old cluster has its access removed once the
storage is migrated.
The ability to move cluster resources between clusters was useful in the past when
moving between OS versions, since a mixed cluster was not possible. I could not have
a Windows Server 2012 cluster and replace nodes with Windows Server 2012 R2.
Instead a new Windows Server 2012 R2 cluster would be created with new hardware
or by removing one node at a time from the old cluster, adding to the new cluster, and
gradually moving over LUNs and the contained VMs or by performing a Shared
Nothing Live Migration between clusters where new storage was available (as a Live
Migration was supported from Windows Server 2012 to Windows Server 2012 R2).
This was a challenging experience, and is not required when moving from Windows
Server 2012 R2 to Windows Server 2016.
Windows Server 2016 enables mixed-mode clusters comprising both Windows Server
2012 R2 and Windows Server 2016 nodes along with the ability to live-migrate VMs